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While computed tomography (CT) represents a tremendous advance in diagnostic imaging, it also creates the problem of incidental detection—the identification of tumors unrelated to the clinical symptoms that initiate the test.To determine the geographic variation in the United States in CT imaging and the corresponding association with one of the most consequential sequelae of incidental detection: nephrectomy.This study is a cross-sectional analysis of age-, sex-, and race-adjusted Medicare data (January 2010-December 2014) from 306 hospital referral regions (HRRs) in the United States and includes information from 15 million fee-for-service Medicare beneficiaries age 65 to 85 years.Regional CT risk (ie, the proportion of the population receiving either a chest or abdominal CT over 5 years).Five-year risk of nephrectomy (partial or total).Data from 15 million fee-for-service Medicare beneficiaries age 65 to 85 years were gathered and illustrate that 43% of Medicare beneficiaries age 65 to 85 years received either a chest or abdominal CT from January 2010 to December 2014. This risk varied across the HRRs, ranging from 31% in Santa Cruz, California, to 52% in Sun City, Arizona. Increased regional CT risk was associated with a higher nephrectomy risk (r = 0.38; 95% CI, 0.28-0.47), particularly among HRRs with more than 50 000 beneficiaries (r = 0.47; 95% CI, 0.31-0.61). After controlling for HRR adult smoking rates, imaging an additional 1000 beneficiaries was associated with 4 additional nephrectomies (95% CI, 3-5). Case-fatality rates for those who underwent nephrectomy were 2.1% at 30 days and 4.3% at 90 days.Fee-for-service Medicare beneficiaries are commonly exposed to CT imaging. Those residing in high-scanning regions face a higher risk of nephrectomy, presumably reflecting the incidental detection of renal masses. Additional surgery should be considered one of the risks of excessive CT imaging.